Investigation of Electrochemical Dissolution Behavior of Near-α TA15 Titanium Alloy in NaCl Solution with Low-Frequency Pulse Current

Abstract

TA15 material is a typical near-α titanium alloy and widely used for the aircraft key load bearing components. Electrochemical machining (ECM) is a cost-effective method to machine difficult-to-cut TA15. Due to the high chemical reactivity of titanium, titanium alloy is prone to passivation, which increases the difficulty of ECM, especially for some common ECM methods with low-frequency pulse currents. To investigate the change of surface characteristics of titanium alloy in pulse ECM, the dissolution behavior of TA15 in NaCl solution under the low frequency pulse current was analyzed by scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS). The results showed that even after removal of initial air-formed oxide film, TA15 would be passivated to form a new passive film during long pulse-off time. Under short pulse-on time, the passive film formed in pulse-off time could not be effectively removed in one pulse-on time, and the passivation effect would be accumulated, resulting in poor machined surface with humps and pits. When the pulse-on time was long enough to completely remove the newly formed passive film, TA15 was dissolved normally to obtain excellent surface with clear crystal structure.